Radio Frequency (RF) power amplifiers (PA) are widely used in particular in wireless communication applications such as e.g. cellular network radio base station amplifiers. With the recent growth in the demand for wireless services, the operating frequency for wireless networks and, as a consequence also for RF PA, has increased dramatically and is now in excess of 2 GHz.
At the high frequencies such RF PA must operate, impedance matching and biasing of the active elements is an important factor for an efficient operation of the RF PA. The input and output circuits used to match power transistors to external devices are typically implemented with a combination of bondwire inductance, in-package capacitors, stripline or microstrip structures on a printed circuit board, and discrete capacitors.
Modern RF power amplifiers typically use RF power transistor devices. Such devices include a semiconductor die being encapsulated in a package which comprises several terminal leads. Such terminal leads include an RF output lead via which the generated RF power is outputted. Further, a so called video lead may be used for connecting a resonance circuit embedded in a package of the RF power transistor device with an external decoupling capacitor. Such an external decoupling capacitor is used for adjusting the video-band resonance frequency of the resonance circuit. The resonance circuit may be used for compensating at least partially parasitic inductances and capacitances with the semiconductor die and the surrounding package.
For connecting this resonance circuit with the external decoupling capacitor one or more bondwires may be used for carrying a so called forward current from the resonance circuit to the video lead. Further, there is provided a current path coursing (a) through ground vias to a backside of a printed circuit board (PCB), (b) over the backside of the PCB, and (c) via a grounded metal block and/or via a grounded flange of the RF power transistor device. This provided current path carries a so called ground return current.
In known packages for RF power transistor devices (a) the current path for the ground return current is quite long and (b) the spatial separation between the forward current flowing though at least one bondwire and the ground return current is quite large. Both given facts (a) and (b) result in an increase of the parasitic inductance of packaged RF power transistor devices. As a consequence, the performance of a packaged RF power transistor device is deteriorated.
U.S. Pat. No. 6,734,728 B1 discloses a broadband RF PA which uses a RF power transistor device with separate terminals for the injection of gate bias and drain bias direct current DC sources. Thereby, the need for ¼ wavelength transmission lines is eliminated and the freed up space can be employed for a higher density packaging. The disclosed RF power transistor device can be implemented with a single die circuit or multiple die circuits operating in parallel.
US 2012/0146723 A1 discloses a high power RF amplifier having output impedance matching networks. Such a high power RF amplifier includes an active semiconductor device mounted on a substrate within a device package. The disclosed RF amplifier has an output impedance matching network comprising a high pass network provided at least partly on the active semiconductor device and a low pass network having a first inductive shunt connection between an output of the active semiconductor device and a first output lead and a second inductive shunt connection between the output of the active semiconductor device and a second output lead. A part of the second output lead forms an inductance contributing to the inductance of the low pass network.
There may be a need for providing a package for a RF power transistor device which yields a high performance of the RF power transistor device within a wide frequency range.